12mm is stuff all, it should be just enough. I would like 15mm ideally then it would have a rake like factory. It should still have a very slight one after that but it won't be noticeable, it will look flat. But with enough time the front should settle down a bit from age and weight of the engine that it should end up looking right in a few years. atm the ass is lower once I filled up, was flat prior to filling the tank so it needs that 12mm for sure. I did measure it by jacking the rear up 6mm and then 12mm. 12mm was just enough.
Going to drop the car this week back to the exhaust guy and he is going to change the tail pipe from the mufflers before the diff to a single 3" tail pipe. This way it will clear the diff upper mount and he is also going to add a resonator. Its not loud at all until you hit the pedal under load and then it's stupid loud! sounds great though

So at least I should not loose the sound too much as it's only a single at the very last stretch and dual most of the way.